These are from the bounce processor. This seems to be implying that there's a syntactically invalid email in the account.

The simplest thing might be to access the email account yourself to delete the email. That said, the email should already have been removed by then (we remove the message before processing it) so it shouldn't keep repeating. Is it repeating every hour or so?

If it's not happening every time, then I'd probably ignore it, though that is more than I would expect.

The problem/challenge is that we need to get access to the message and to prevent situations where a bad email causes permanent looping, we delete the message from the server before processing it. (If we didn't do that, this error would have broken the handler continuously.) If it comes back, we may get need to get some logging code in so we can see the full email.